Improving the performance of the time-of-arrival estimator in MIMO systems

With the objective of minimizing the Cramer-Rao lower bound (CRLB) of the time of arrival (ToA) estimator, we propose a method to improve the accuracy of ToA estimate for multiple-input multiple-output (MIMO) systems when the transmitted signal can be pre-processed. Transmit beamforming is adopted when the channel state information at the transmitter (CSIT) is available, while space time block code (STBC) is utilized as the transmit diversity technique for the case of unavailable CSIT. Under the assumption that the channel state information at the receiver (CSIR) is always available for both cases, we employ receive beamforming at the receiver. We demonstrate through simulation that the performance of ToA estimator is enhanced with the availability of CSIT, and further improved with the increase of antenna number. Under the condition of erroneous CSIT, improvement can still be observed compared with the case of unavailable CSIT when the signal to noise ratio (SNR) is below a threshold.